This invention relates to a storage system to store data used by computers and, and more specifically to a storage system that allows the capacity of storage accessed by computers to be changed.
The storage capacity of a conventional storage system depends on the capacity of disk drives or other similar physical devices installed in the system. Therefore, when required to have a large storage capacity, a storage system has to be equipped with an accordingly large number of physical devices. While there is a demand for a large storage capacity, users also make a conflicting demand for reduction in cost and size.
Here comes an urgent need to develop a mechanism that enables a storage system to change its storage capacity dynamically. One of methods known to be useful in building such a storage system is automatic storage device capacity expansion (see JP 2003-15915 A, for example). In this method, a logical block address in a read or write I/O request at which a host computer accesses a logical volume of a storage device is monitored. Then, with the obtained logical block address as the key, the storage area of the logical volume is dynamically expanded. This method also allows a command unit of a host computer to send a logical volume capacity reduction/expansion instruction to a volume server, which then reduces/expands the storage area of the logical volume.